Learn more about mRNA and how it is used in the development of vaccines.

Updated Dec. 21, 2020

Experts are optimistic about preliminary results from mRNA COVID-19 vaccine candidates. A Phase 3 clinical study suggested Pfizer-BioNTech’s candidate, BNT162b2, was 95% effective in preventing COVID-19 in participants. Soon after Pfizer’s announcement, preliminary interim data from Moderna suggested that its vaccine is 94.5% effective.

On December 11, 2020, the Food and Drug Administration (FDA) granted an emergency use authorization (EUA) for the Pfizer vaccine candidate to be used against COVID-19 in the U.S. It became the first-ever mRNA-based vaccine to gain regulatory authorization. The Moderna vaccine received an EUA on Dec. 18.

There’s potential that mRNA-based vaccines will be faster to produce than traditional vaccines, an enormous benefit as the pandemic rages. But what is mRNA, and what makes vaccines that use this molecule different?

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What Is mRNA?

mRNA stands for messenger ribonucleic acid. They’re single-stranded molecules that carry genetic code from DNA in a cell’s nucleus to ribosomes, which make protein in the cells. These molecules are called messenger RNA because they carry instructions for producing proteins from one part of the cell to another.

How mRNA delivers messages in three steps:

  1. A process known as transcription makes an RNA copy of a DNA sequence for a protein.
  2. This copy, known as mRNA, moves from the nucleus (center) of the cell to the ribosomes. Ribosomes, which are located in the cell outside of the nucleus, make proteins.
  3. Ribosomes “translate” the instructions in mRNA and synthesize the protein.

How Does an mRNA Vaccine Work?

Pfizer (in partnership with BioNTech) and Moderna are both working on COVID-19 vaccines using mRNA.

Scientists engineered a synthetic mRNA that codes for the spike protein on the coronavirus. This is the part of the virus that helps it enter human cells. The spikes are what you see on illustrations of the SARS-CoV-2 viral particle.

This synthetic mRNA instructs cells in the human body to make their own viral spike protein. This triggers the immune system to make antibodies to fight the virus. Once the immune system knows how to make these antibodies, it can do it again when exposed to the spike protein.

You can think of an mRNA vaccine as sending instructions into the body on how to fight COVID-19. Once the body makes the viral proteins, the immune system learns how to destroy them. This gives your body the tools to defend against SARS-CoV-2 if you’re exposed.

Lipid nanoparticles

Lipid nanoparticles are necessary in the manufacture of mRNA vaccines. Scientists encase mRNA inside a pod made of oily lipids, which allow mRNA to more easily slide into cells.

How Do mRNA Vaccines Differ From Traditional Vaccines?

The goal of any vaccine is to train your body to recognize and fight germs by producing antibodies and activating immune cells.

Conventional vaccines introduce weakened, dead, or noninfectious parts of a virus or bacterium to the body. By contrast, mRNA vaccines give the body instructions for making its own viral or bacterial proteins, which the immune system then responds to.

Benefits of mRNA vaccines to traditional vaccines

  • There is no risk of infection by the vaccine because mRNA vaccines do not introduce a live virus to the body.
  • Unlike conventional vaccines, mRNA vaccines are not grown in live cells, which speeds up the manufacturing process. mRNA vaccines also bypass the step of inactivating viruses or isolating the protein, which also makes them quicker to produce.
  • mRNA vaccines are more effective against germs that evolve through mutation. That’s because RNA vaccines typically trigger an immune response to a part of the virus (the viral stalk) that doesn’t mutate easily. Traditional vaccines typically target a different part of the virus (the globular head), which does mutate easily.

Other Facts About Potential mRNA COVID-19 Vaccines

Both mRNA and lipid nanoparticles are unstable and sensitive to heat. The mRNA vaccine candidates from Pfizer and Moderna must ship frozen. Transportation and storage of the vaccines require heat-mitigating tactics, such as the use of cold shippers and dry ice.

Both Pfizer and Moderna’s mRNA vaccine candidates will need two doses per person over time.


The Science and Fundamentals of mRNA Technology. Moderna. Link

Why so many people are hopeful about an mRNA coronavirus vaccine. CNBC. Link

Moderna's mRNA vaccine reaches its final phase. Here's how it works. National Geographic. Link

Vaccine Chaos Is Looming. The Atlantic. Link

Pfizer and BioNTech Announce Vaccine Candidate Against COVID-19 Achieved Success in First Interim Analysis from Phase 3 Study. Pfizer. Link

How Scientists Could Stop the Next Pandemic Before It Starts. The New York Times. Link

Candidate for universal flu vaccine protects against multiple strains. Science Daily. Link

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